I download apps for my Mac from the Mac App Store whenever possible. Going through the Mac App Store gives me a piece of mind knowing Apple screens all submissions and keeps harmful software at bay.
But every once in a while, an app comes along and gets distributed outside the Mac App Store's safe haven. True, one can verify signing information for non-Mac App Store apps in Terminal, but it isn't for the faint-hearted.
That's precisely the kind of problem that a nifty little Mac app, called Suspicious Package, solves in one fell swoop.
Created by a company called Mothers Ruin Software, the free of charge app is actually a plug-in for the Mac's Quick Look feature, allowing you to easily and quickly inspect contents of a .PKG installer file after you've downloaded it but before it's launched.